This invention relates to heat exchangers and, more particularly, to a plurality of heat pipes which provide an effective coupling of heat from a source to a heat sink.
A heat pipe is a simple, mechanically static, closed or sealed chamber containing a working fluid having both a liquid phase and a vapor phase within the desired range of operating temperatures. In such a heat pipe, air or other non-condensable gases are usually evacuated from the sealed chamber. The chamber then contains only the liquid and vapor of the working fluid at a pressure corresponding to the saturation pressure of the working fluid at the temperature of the heat pipe. When one portion of the chamber containing liquid is exposed to a relatively high temperature it functions as an evaporator section. The resulting heat flow will cause evaporation to take place resulting in an increase in the vapor pressure of the working fluid. A vapor that is formed, being at a higher pressure, will flow towards the colder regions of the chamber, defined as a condenser section, and will condense on the relatively cooler surfaces inside the chamber wall. Capillary action and/or gravitational flow will return the liquid condensate to the evaporator section. Because the heat of evaporation is absorbed by the phase change from liquid to vapor and released when condensation of the vapor takes place, large amounts of heat can be transported with very small temperature gradients from areas of heat addition to areas of heat removal.
Heat pipes are generally made as individual tubes and clustered together where additional capacity is required. These heat pipes are used in connection with the heating and cooling of various devices or structures. For example, U.S. Pat. Nos. 3,865,184 and 4,440,215 illustrate the use of heat pipes in a regenerator to exchange heat between intake air as it flows into an enclosure and exhaust air as it flows out of the enclosure. Generally, these heat pipes are arranged in a shell in a horizontal array with wick members to aid in the liquid transport from condenser to evaporator. However, the heat pipes may be constructed without wicking members if the condensate section is slightly elevated above the evaporator section. In the prior art source and sink fluids typically flow transverse to the longitudinal axis of the heat pipes but in the same direction. Other prior art devices had the evaporator heat pipes connected to a common manifold and the condenser heat pipes connected to another common manifold, whereby the two manifolds were in fluid communication. Accordingly, these heat pipes were at the same pressure and connected in a parallel flow arrangement. This parallel flow is a major factor in the low efficiency of such previously devised heat pipe heat exchangers. This lower efficiency is caused by a non-uniform temperature difference between the two fluids which results from a parallel flow arrangement. A counter flow arrangement, however, would take advantage of the most uniform temperature difference between the sink and source fluid streams thus utilizing the heat transfer surfaces most effectively.
Thus it would be desirable to provide a heat exchanger which overcomes the problems of the previously devised heat pipe heat exchangers relating to less than maximum heat transfer efficiency.